Ultrasonic microphones may be used to detect a position of an ultrasound emitting stylus. The microphones used typically utilize the inherent mechanical resonance of small-sized micro-electro-mechanical system (MEMS) structures in order to make a small and inexpensive receiver. The resonance frequency is on the order of 35 to 55 kilohertz (kHz).
The microphones are typically sampled at least twice the largest frequency used (Nyquist criterion) a frequency larger than the resonance frequency. For example, sampling frequencies of 96 kHz or 192 kHz are common, resulting in a relatively large current consumption and low electromagnetic interference (EMI) immunity. An ultrasonic microphone with digital output would similarly suffer from high current consumption due to a large sample rate and a large bandwidth needed to transfer data.